OBJECTIVE: To understand the dynamics of accommodation and presbyopia RESULTS We implanted an electrode into the Edinger-Westphal nucleus of iridectomized rhesus monkeys between the ages of 8 and 16 yr. We determined baseline real-time dynamics of ciliary muscle, lenticular and zonular movement in response to midbrain stimulation by digital image analysis of Scheimpflug slit lamp and goniovideographic recordings. We performed various surgical ablations including extra-and intra-capsular lens extratcion, posterior capsulotomy and complete posterior capsulectomy following extracapsular lens extraction and regional zonulolysis, and have recorded some preliminary alterations in baseline real-time accommodation dynamics. These studies are generating new information about the pathophysiology of presbyopia in the rhesus monkey, the only known animal model for the human condition. FUTURE DIRECTIONS Further analysis will be done on images recorded from the surgically manipulated eyes to determine the role of the ablated structures in the accommodative process. KEY WORDS ciliary muscle, lens, zonule, capsulotomy , zonulolysis, midbrain, aniridia, electrode